The present invention relates to air sampling (collection) devices, particularly to portable air sampling systems for the rapid detection and analysis of pathogenic organisms, and more particularly to a portable or stationary high air volume to low liquid volume collector for aerosol particles.
As the threat of biological weapons increases, both in military theaters and civilian populations, the need for portable or stationary systems for the rapid detection and analysis of pathogenic organisms becomes increasingly important. The first step in any system for detection and characterization of biological agents is a sample collector. This can take on the simple form of a cotton swab for solid surfaces, or as in the case of airborne pathogens, an aerosol sample collector is used to collect and concentrate airborne particulate into a liquid sample volume for subsequent preparation and analysis. An aerosol sampler is the most appropriate for continuous monitoring scenarios, where repeated swabbing of settled particles is impractical. Most commercial samplers now available for field use are large, power consuming, and produce collected sample into large volumes of liquid, typically  greater than 10 mL. Emerging miniature detection systems analyze much smaller sample volumes, typically  less than 250 xcexcL. When using the presently available air samplers, the sample volume must be xe2x80x9csub-sampledxe2x80x9d, effectively diluting the sample, resulting in a loss of sensitivity of detection. Thus, there is a need for a collector which will collect particulate at a high airflow and yet utilize a low liquid volume.
The present invention provides a solution to the above need by providing a collector which can collect airborne particulate at a high air flow rate and yet has been designed so that the resultant delivered liquid volume is 100-300 xcexcL, preferably only 200 xcexcL or less. This invention also addresses the problem of dilution because of sub-sampling. The size, weight and low power specifications of this aerosol sampler will closely match the current state-of-the-art in pathogen detection systems and ease the deployment in remote locations. The collector of this invention utilizes high air volume to low liquid volume (preferably 200 xcexcL) for aerosol particles.
It is an object of the present invention to provide a high air volume, low liquid volume aerosol collector.
A further object of the invention is to provide a collector for aerosol particles having a high volume flow wherein the particles are drawn into a small volume of liquid (e.g., 200 microliter).
Another object of the invention is to provide a small, low power, high efficiency air sampling or collection device.
Another object of the invention is to provide a portable or stationary high air volume to low liquid volume collector for use with biological or other airborne material collection.
Another object of the invention is to provide an aerosol collector wherein a high volume flow of aerosol particles is drawn into an outer annular slot in the collector and is directed into a small volume of liquid located in a central lower section of the collector, and is provided with means for preventing loss of the collecting liquid and means for controlling the volume of the collecting liquid.
Other objects and advantages will become apparent from the following description and accompanying drawing. The invention is a high air volume to low (100-300, preferably 200 xcexcL) liquid volume aerosol collector. A high volume flow of aerosol particles (e.g., 225 Lpm) is drawn into an annular, centripetal slot (e.g., 1 to 2 mm wide) located in an outer portion of a collector housing, and which directs the aerosol flow into a small volume (e.g., 200 xcexcL) of collection liquid located in a lower central portion of the housing. The annular jet of air impinges into the collection liquid pool, imbedding the airborne particles therein in the liquid. The air jet passes through the collection liquid and is discharged from the housing via an upper side opening. The collection liquid continuously circulates by moving to the center of the collector housing, then upwardly, and through assistance by a rotating deflector plate falls back onto the liquid pool above the impinging air jet. Any liquid droplets escaping with the effluent air are captured and moved back toward the liquid pool by a rotating mist eliminator placed above the liquid pool. As liquid is evaporated from the collecting liquid due to the airflow, the required makeup liquid is continuously added through a drain port at the bottom of the collection liquid pool. The amount of makeup liquid is calculated by computer from the difference in the relative humidity measured at the collector air inlet and outlet. To maintain the appropriate amount of collecting liquid, the liquid collected by the mist eliminator is drained back down through a sensor, which measures the liquid flow through it. The sensor can also be used to measure whether the collecting liquid level in the collector is higher or lower than the height of the sensor when the airflow is turned off. This will then activate additional liquid inflow or reduction in inflow. A syringe may be used to extract the liquid above the desired final collecting liquid volume. The liquid can then be drained back in so that the collector can be operated until the liquid has evaporated to the desirable final collecting liquid volume, e.g., 200 microliter.